[5] Conformation-specific antibodies: approach to the study of the vitamin K-dependent blood coagulation proteins

Conformation-specific monoclonal antibodies directed against the calcium-stabilized structure of human prothrombin

“…A fundamental and unanswered question relates to the molecular basis of antibody recognition of a particular three-dimensional form of a macromolecule (Furie et al, 1982). One hypothesis suggests that antibody binding to a specific protein conformer stabilizes that conformer and facilitates recognition and binding by a second antibody to a second antigenic site.…”

Immunoradiometric Assay for the Calcium-Stabilized Conformation of Human Protein S

“…Recently published observations indicated that additional high affinity Ca(II) binding sites in Gla domainless thrombin-modified protein S exist (19). Binding of Ca(II) to other vitamin In dependent factors [prothrombin (23,30), factor VII (24,25) and factor IX (27,28,29)] results in the formation of a Ca(II)stabilized structure (13,14,15,16) that contain unique epitopes, that will be recognized by specific antibody preparations. From a previously obtained rabbit antiserum against human protein S (31), we could isolate an antibody subpopulation that binds to protein S in the presence of Ca(II), but does not bind in the presence of EDTA.…”

“…During vitamin K deficiency or in the presence of vitamin K antagonists y-carboxylation of the vitamin K-dependent proteins (including protein S) will be (partly) inhibited, thus leading to the production of both normal and non-and subcarboxylated molecu les. For prothrombin (21)(22)(23), factor VII (24,25) and factor IX (26)(27)(28)(29) it has been shown that reduced y-carboxylation will result in defects both in Ca(II) binding and in the formation of Ca(II)dependent conformational changes, thus leading to reduced functional activity. As a result the ratio of activity over antigen will decrease for these plasma proteins.…”